The present invention relates to a magnetic recording and reproducing apparatus such as a video tape recorder (hereinafter, referred to as a VTR) for recording or reproducing a signal to/from a magnetic tape with a rotary magnetic head or the like. The invention particularly relates to a construction of a variable speed reproducing signal processing section in a digital type magnetic recording and reproducing apparatus such as a digital type VTR for recording or reproducing a digital signal or the like.
Hitherto, in an analog VTR, there has been proposed a construction (hereinafter, referred to as a movable head type) in which in a variable speed reproducing mode, that is, in a mode to reproduce a signal in a state in which a magnetic tape is moved at a running speed different from a standard speed, a rotary magnetic head for signal reproduction is controlled in a rotary shaft direction on a rotary cylinder and is moved and deviated by a micro amount, thereby allowing the signal reproducing rotary magnetic head to be always correctly scanned on a video signal track. According to the construction, the signal reproducing rotary magnetic head is not scanned in a state in which the head rides over a plurality of video signal tracks. Therefore, no noise bar is generated on a reproducing screen such as a screen of a television receiver or the like and what is called a noiseless variable speed reproduction image is obtained. A piezoelectric element or the like is used as means for moving and deviating the position of the signal reproducing rotary magnetic head. In the construction using a piezoelectric element, the signal reproducing head is mounted on the piezoelectric element and a voltage which is applied to the piezoelectric element is controlled so that the position in the direction of the rotary shaft of the signal reproducing rotary magnetic head is controlled in proportion to the applied voltage. Even in the case of using another deviating element of the piezoelectric element as head movement deviating means, a construction which is almost similar to the above construction is used. The above movable head type is frequently used in, particularly, a field such as a broadcasting station in which variable speed reproduction of a high picture quality is required. In the above convential techniques, a waveform of an applied voltage to deviate the rotary magnetic head mainly comprises two kinds of signals. The first kind of signal is a signal to correct for deviation of an angle of inclination of a scanning locus of the signal reproducing rotary magnetic head to a magnetic tape from an inclination angle of a recording track as the tape speed is deviated from the ordinary standard speed due to the variable speed reproducing mode. A signal waveform in this case is a triangular wave having the same period as that of a switching signal of the head. The second kind of signal is a signal for moving the rotary magnetic head in parallel by only the track deviation amount in order to allow the rotary magnetic head to correctly scan on the track. The second signal has a waveform whose signal level is changed at the same period as that of the switching signal of the rotary magnetic head.
Several methods are at present proposed as a method of forming the applied voltage waveform. Two typical methods in the conventional analog VTR are described below. In the first method, a period of pulses in a capstan FG (Frequency Generator) signal is changed in accordance with a tape speed and a control signal recorded in the longitudinal direction of a magnetic tape are used. An example of a construction of the first method has been disclosed in, for instance, JP-B-63-19929. In the second method, a reproducing timing of a vertical sync signal and a period of a horizontal sync signal which are reproduced from a magnetic tape by a rotary magnetic head for reproduction are detected and an applied voltage waveform is produced.
According to both of the first and second methods, the tape running speed and the phase relation between the rotary magnetic head and the tape are derived from the detected information, respectively, and the applied voltage waveform to correct an angle deviation and a position deviation of the head locus is formed.
The movable head control techniques in the conventional analog VTR have been described above. Further, it is a future subject that the above techniques are applied to a digital VTR and a range in which the noiseless variable speed reproduction can be executed is further widened, and the performance is improved.
In the conventional analog type VTR, for instance, in a one-inch C-format VTR or the like, a video signal of one field is recorded onto one track. To apply the above movable head method to such a VTR in a noiseless manner, it is necessary to control the reproducing magnetic head so as to accurately scan on the video track in which one track is set to a unit. Further, in the digital VTR, if a video signal is converted into a digital signal with the high picture quality information held, an amount of information increases. Therefore, the video signal information of one field is generally divided and recorded onto a plurality of tracks. For instance, consideration will now be made with respect to a recording format in which the signal of one field has been divided and recorded onto six contiguous tracks. In such a format, in order to execute the noiseless variable speed reproduction, no only must the reproducing magnetic head be accurately scanned on one track but also the reproducing magnetic head must be controlled so as to be accurately scanned on all of the six contiguous tracks corresponding to one field.
To apply the conventional first method in which the rotary magnetic head is controlled by the control signal recorded in the longitudinal direction of the magnetic tape to the digital VTR, it is an inevitable condition to obtain the address information (information indicative of which number of track of which field) of each track from the control signal.
On the other hand, consideration will now be made with respect to the case where the conventional second method in which the rotary magnetic head is controlled by the timings for producing the reproduced horizontal and vertical sync signals is applied to the digital VTR. As mentioned above, in the digital VTR, an information amount is so large that the signal of one field must be recorded onto a plurality of tracks. Therefore, it is an effective method that data which is recorded onto a magnetic tape is reduced as little as possible while keeping the image data as it is. As one of the methods which are ordinarily used, there is a method whereby signals which appear in the video signal at predetermined periods, for instance, horizontal and vertical sync signals, a color burst signal, and the like, are not recorded onto the magnetic tape.
In the digital VTR using such a method, none of the horizontal sync signal, vertical sync signal, and the like is included in the signal reproduced from the rotary magnetic head. Therefore, in such a type of digital VTR, unless signals in place of those signals exist, the conventional type of movable head system cannot be applied. Further, since the signal of one field is recorded onto a plurality of tracks, the address information of each track must be obtained from the reproduction signal.